Air evacuating ventilator

ABSTRACT

The invention concerns a ventilator comprising a cylindrical housing the intake of which is connected to a coaxial cylindrical conduit of smaller diameter, an electric motor axially mounted in the housing, of small diameter relative to that of the housing, and on the shaft of which is fixed a wheel consisting of blades, each having a shape that all the cross-sections of a blade through planes parallel to the axis of the housing are parallel to said axis and the vanes orienting the air stream, integral with the inner side of the housing, distributed at the periphery of the housing and each including at least a curved part which, located on the side of the housing intake, is housed in an annular space comprised between the housing and the virtual cylindrical surface extending the air intake.

[0001] The present invention relates to a fan designed to be associatedwith a duct for extracting air from at least one room, to provide airrenewal in the room.

[0002] Many rooms, whether used for living accommodation or for offices,have devices providing air renewal, with the purpose of keeping therooms in good condition, since they must be ventilated to ensure thattheir constituent materials retain their properties, and also for thepurpose of providing comfort for the occupants.

[0003] Present-day rooms are generally provided with controlledmechanical ventilation installations, such installations comprising anextraction unit designed to extract a certain volume of air from roomscontaining sanitary and cooking facilities, such as kitchens, bathrooms,toilets, etc., an equivalent volume of air to that which has beenextracted being admitted into living accommodation such as lounges orbedrooms through air intakes provided in these rooms, in the windowframes for example.

[0004] Another solution, implemented particularly in older buildings,consists in the provision of an air outlet in the sanitary and cookingrooms leading to a duct with a large cross section, opening at rooflevel, the air being extracted by natural draft when the motive pressuredue to the wind and to thermal circulation is sufficient, for examplewhen this motive pressure is greater than that generated by the combinedaction of a temperature difference of 10° C. between the interior andthe exterior of the rooms and a wind of 3 m/s. The natural draft canprovide satisfactory results in winter when the external temperature issignificantly higher than the temperature inside the room. However, inthe summer there may be a temperature inversion, causing air tocirculate in the reverse direction, in other words with air enteringthrough the duct normally used for extraction.

[0005] It may therefore be useful to associate this duct with a fan, toprovide a supplementary motive pressure when the natural draft isinsufficient, particularly in the summer, by using an axial fan having aplurality of blades extending outward from the fan shaft, these bladeshaving an inclination which causes a displacement of air. However, aconsiderable amount of motive power must be provided to drive the fan,and, when the fan is stationary to permit air renewal by natural draft,the blades create a significant pressure drop which considerably limitthe flow of extracted air.

[0006] The object of the invention is to provide a fan designed to beassociated with an air extraction duct whose structure is such that thefan creates only negligible pressure drops when it is stationary, thuspermitting air extraction by natural draft, and which, when inoperation, provides an air flow comparable to that obtained with anormal natural draft corresponding, for example, to a temperaturedifference of 15° C. between the interior and the exterior and a windspeed of 4 m/s, while having very low electricity consumption, thusenabling it to be supplied, if required, by a solar panel placed on theroof beside the fan. The object of the invention is therefore to providean installation which runs permanently on natural energy, in other wordsthe motive pressure due to the wind and to thermal circulation,particularly in the winter and in the intermediate seasons, and on solarenergy which supplies the fan motor in the summer.

[0007] For this purpose, the The fan as claimed in the inventioncomprises:

[0008] a cylindrical shell whose inlet is connected to a coaxialcylindrical duct of smaller diameter by a radial shoulder;

[0009] an electric motor mounted axially in the shell, and having asmall diameter in relation to that of the shell, an impeller consistingof blades being fixed on the motor shaft, each blade being shaped insuch a way that all the cross sections of one blade in planes parallelto the axis of the shell are parallel to the said axis, the maximumdiameter of the blades being between the diameter of the shell and thatof the inlet of the shell and decreasing in the downstream direction, inother words from the inlet end to the other end, and

[0010] air guide vanes, integral with the inner surface of the shell,distributed over the periphery of the shell and comprising in each caseat least one curved part which, being located at the inlet end of theshell, is housed in the annular space between the shell and the virtualcylindrical surface which extends the air inlet.

[0011] Because of the shape of the blades of the fan impeller, theseblades offer only a very low resistance to the flow of air and generateonly small pressure drops when the motor is stopped. As regards theguide vanes, their curved part is located in an area outside the flow ofair, since the inlet surface of the shell is smaller than the surface ofthe shell. However, the The fan as claimed in the invention is highlyeffective when the electric motor drives the impeller, since the airmoved by the impeller strikes the guide vanes which channel the air fromupstream to downstream. The efficiency of this fan is very high and itsconsumption is low, enabling the motor to be supplied with solar energy.

[0012] In one embodiment of this fan, each blade is flat and iscontained in a longitudinal plane including the axis of the shell.

[0013] In a possible embodiment, each blade has an inlet edge which isperpendicular to the axis of the shell and is extended from the point ofthe outlet edge of the blade located farthest upstream.

[0014] The outlet edge of each blade is at a maximum distance from theaxis of the shell at the level of its junction with the inlet edge, andthen follows a curve which, in the downstream direction, progressivelyapproaches the axis of said shell.

[0015] In such a case, the surface area of each blade decreases in thedownstream direction.

[0016] In another possible embodiment, each blade has an inlet edgeperpendicular to the axis of the shell, which extends from the point ofthe outlet edge of the blade located farthest upstream over a part ofthe radius of the shell, this edge being extended by an edge running inthe downstream and inward direction, thus delimiting a blade in thegeneral shape of a half-crescent.

[0017] Thus it is possible to have a blade whose width increases in thedownstream direction.

[0018] According to another characteristic of the invention, theupstream end of each guide vane is located in the proximity of the pathof the upstream parts of the outlet edges of the blades, each vanehaving a curved part, in other words a part not extending axially withrespect to the shell, and having an angle of attack whose orientation issimilar to that of the air jets emerging from the blades of theimpeller, and being located outside the main flow in natural draftconditions when the fan is stationary, and extending, for example, overa length approximately equal to the diameter of the inlet of the shell,each curved part being extended in the downstream direction by a flatpart parallel to the axis of the shell.

[0019] It should be noted that, in natural draft conditions, the flow ofair, which at the level of the inlet occupies the cross section of theinlet, is broadened only slightly downstream, over a distance equal tothe diameter of the inlet. Therefore the curved parts of the guide vanescause practically no perturbation of the air flow. Beyond this distance,the air flow is in contact with parts of vanes which are parallel to itand which resist it only to a negligible degree. At this level, thevanes can also be wider and their inner sides can enter the virtualcylinder located in the extension of the inlet of the shell.

[0020] In any case the invention will be clearly understood from thefollowing description which refers to the attached schematic drawingrepresenting, without restrictive intent, an embodiment of this fan.

[0021]FIG. 1 is a highly schematic view of a building equipped with aventilation duct fitted with this fan;

[0022]FIG. 2 is a perspective view of the fan;

[0023]FIG. 3 is a view in longitudinal section;

[0024]FIG. 4 is a view in cross section along the line IV-IV of FIG. 3.

[0025]FIG. 1 represents a building, indicated by the general reference2, containing a plurality of superimposed rooms 3, each room having atleast one outlet 4 communicating with a vertical ventilation duct 5opening at the level of the roof 11 of the building. The upper part ofthe duct 5 is connected to a cylindrical shell 6 having a largerexternal diameter, the inner part of the shell being joined to the ductby a radial shoulder 7. Thus the inlet 8 of the shell, having a crosssection identical to that of the duct, is smaller than the cross sectionof the shell 6. An electric motor 10 having a cross section much smallerthan that of the shell is fixed by means of a plurality of radial bars 9in the shell 6, the diameter of the motor body being, for example,between 10% and 20% of the diameter of the shell. An impeller 13 havinga plurality of blades 14 is keyed onto the shaft 12 of the motor, whichis central and coaxial with respect to the shell 6. Each blade consistsof a flat plate whose inlet edge 15 is perpendicular to the axis of theshell and whose outlet edge 16 progressively approaches the axis of theshell in the downstream direction. It should be noted that the outer end17 of the inlet edge 15 of each blade 14 faces the radial shoulder 7.The clearance between the edge 15 and the shoulder 7 is as small aspossible. In a variant embodiment, each blade has an inlet edge 15 withan outer part perpendicular to the axis of the shell which is extendedby another part following, in the downstream direction, the curved line18 represented in FIGS. 2 and 3, thus forming a blade in the generalshape of a half-crescent whose width can increase in the downstreamdirection.

[0026] Guide vanes 19 for the air flow are fixed on the walls of theshell 6, facing the impeller and downstream from it. Each vane 19 has afirst part 19 a extending to a distance from the inlet 8 which isapproximately equal to the diameter of the inlet. This part 19 a of thevane, which is contained in the space delimited by the cylindrical shell6 and a virtual cylinder extending the inlet 8 of the shell, is curvedand has an angle of attack whose orientation is similar to that of theair jets emerging from the blades of the impeller. This part 19 a isextended in the downstream direction by a flat part 19 b parallel to theaxis of the shell.

[0027] This device operates in the following way.

[0028] In natural draft operation, the flow of air at the inlet of thestationary impeller 13 is parallel to the planes of the blades 14, andthe path through said impeller, which does not divert the flow, has anegligible resistance to the passage of the air.

[0029] It should also be noted that, because of its inertia, the airflow which occupies the whole inlet cross section does not undergosignificant expansion until it is downstream of the curved parts of theguide vanes. There is practically no contact between the air flow andthese vanes except in their flat parts parallel to the axis of theshell, which have only a very low resistance to the flow of the air.

[0030] When the fan is in operation, it should be noted that thevelocity Vs of the air flow at the impeller outlet is similar to theresultant of the inlet velocity Ve and the impeller rotation velocity Vrat the level of its outlet point.

[0031] The impeller can exert a dynamic pressure on the air of this flowwith a kinetic energy equal to 0.5×ρ×Vr² where ρ is the density of theair.

[0032] As the distance from the axis of the shell increases, thevelocity Vr also increases, the dynamic pressure exerted on the air isintensified, and the orientation of the air is diverted increasinglytoward the walls of the shell.

[0033] The intake guide vanes 19 a channel the fastest peripheral airjets leaving the impeller 13, to progressively convert their rotarymovement into a longitudinal displacement which increases the usefuloutput and pressure provided by the fan. These guided flows which havethe strongest dynamic pressures share part of their energy with theflows emerging from the parts of the impeller closest to its axis, andby induction cause them to occupy the whole passage surface of the shellin a more uniform way.

[0034] It should be noted that the diameter of the impeller 13 decreasesin the downstream direction to promote the circulation of the air in thedesired direction. The upstream part, having a larger diameter, exertsmore pressure on the air than the downstream part. This arrangement alsomakes it possible to increase progressively the path provided betweenthe impeller 13 and the shell 6 to adapt it to the increasing quantityof air emerging from the impeller as the distance from its inlet 8increases.

[0035] The path through the impeller 13 and consequently the time forwhich it acts on the air increase in length as the axis is approached.The velocity at which the air is driven therefore becomes closer to thevelocity of the impeller as the axis is approached. This solutionattenuates the pressure differences between the peripheral parts and thecentral parts which might generate parasitic return flows.

[0036] As the foregoing description shows, the invention greatlyimproves the prior art by providing a fan having a simple structure, inwhich the blades cause only a small pressure drop and the curved partsof the guide vanes are outside the air flow when the fan is stationary.It is therefore possible to provide air extraction by natural draft whenthe temperature and wind conditions permit. When the temperature andwind conditions do not create sufficient natural draft, the fan canprovide air extraction with a very low electricity consumption, makingit possible to supply the electric motor with solar energy.

[0037] Clearly, the invention is not limited to the embodiment of thisfan described above by way of example, but includes all variantembodiments. Thus, in particular, it would be possible for the shapes ofthe blades to be different, and for each blade not to be flat, withoutthereby departing from the scope of the invention.

1) A fan designed to be associated with a duct for extracting air fromat least one room, to provide air renewal in the room, characterized inthat it comprises: a cylindrical shell (6) whose inlet (8) is connectedto a coaxial cylindrical duct (5) of smaller diameter by a radialshoulder (7); an electric motor mounted axially in the shell (6), andhaving a small diameter in relation to that of the shell, an impeller(13) consisting of blades (14) being fixed on the motor shaft, eachblade being shaped in such a way that all the cross sections of oneblade in planes parallel to the axis of the shell are parallel to thesaid axis, the maximum diameter of the blades (14) being between thediameter of the shell (6) and that of the inlet (8) of the shell anddecreasing in the downstream direction, in other words from the inletend to the other end, and air guide vanes (19), integral with the innersurface of the shell (6), distributed over the periphery of the shelland comprising in each case at least one curved part (19 a) which, beinglocated at the inlet end of the shell, is housed in the annular spacebetween the shell (6) and the virtual cylindrical surface which extendsthe air inlet (8).
 2. The fan as claimed in claim 1, characterized inthat each blade (14) is flat and is contained in a longitudinal planeincluding the axis of the shell.
 3. The fan as claimed in claim 2,characterized in that each blade (14) has an inlet edge (15) which isperpendicular to the axis of the shell (6) and is extended from thepoint of the outlet edge of the blade located farthest upstream to theaxis of the shell.
 4. The fan as claimed in claim 2, characterized inthat each blade (14) has an inlet edge (15) perpendicular to the axis ofthe shell, which extends from the point of the outlet edge of the bladelocated farthest upstream over a part of the radius of the shell, thisedge being extended by an edge (18) running in the downstream and inwarddirection, thus delimiting a blade in the general shape of ahalf-crescent.
 5. The fan as claimed in one of claims 1 to 4,characterized in that the upstream end of each guide vane (19) islocated in the proximity of the path of the upstream parts of the outletedges of the blades, each vane having a curved part (19 a), in otherwords a part not extending axially with respect to the shell, and havingan angle of attack whose orientation is similar to that of the air jetsemerging from the blades of the impeller, and being located outside themain flow in natural draft conditions when the fan is stationary, andextending, for example, over a length approximately equal to thediameter of the inlet of the shell, each curved part being extended inthe downstream direction by a flat part (19 b) parallel to the axis ofthe shell.